Neuromuscular Control

Question 1

What are alpha motor neurons?

Answer 1

lower motor neurons of the brainstem and the spinal cord

Question 2

Alpha motor neurons innervate what?

Answer 2

extrafusal muscle fibres of the skeletal muscles

Question 3

Define a motor unit.

Answer 3

a single motor neuron together with all the muscle fibres that it innervates

Question 4

Define a motor pool.

Answer 4

contains all alpha motor neurons innervating a single muscle

Question 5

Describe type I motor units.

Answer 5

slow
smallest diameter cell bodies
small dendritic trees
thinnest axons
slowest conduction velocity

Question 6

Describe type IIA motor units.

Answer 6

fast, fatigue resistant
larger diameter cell bodies
larger dendritic trees
thicker axons
faster conduction velocity

Question 7

Describe type IIB motor units.

Answer 7

fast, fatiguable
larger diameter cell bodies
larger dendritic trees
thicker axons
faster conduction velocity

Question 8

How are the three motor unit types classified?

Answer 8

amount of tension generated
speed of contraction
fatiguability

Question 9

How is muscle force regulated?

Answer 9

recruitment

rate coding

Question 10

How are motor units recruited?

Answer 10

size principle - smaller units are recruited first

Question 11

What is rate coding?

Answer 11

as firing rate of motor units increases, the force produced by the unit increases

Question 12

What are neurotrophic factors?

Answer 12

a type of growth factor
Prevent neuronal death
Promote growth of neurons after injury

Question 13

Are motor unit and fibre characteristics are dependent or independent on the nerve which innervates them?

Answer 13

dependent e.g. cross innervation

Question 14

Type IIB fibres can change to type IIA fibres most commonly by?

Answer 14

training

Question 15

Type I fibres can change to type II fibres possible by?

Answer 15

severe deconditioning or spinal cord injury

microgravity in space flight

Question 16

Ageing is associating with what change in muscle fibre?

Answer 16

loss of type I and II fibres but also preferential loss of type II fibre

Question 17

What is an involved in an automatic response to a stimulus?

Answer 17

a nerve impulse passing inward from a receptor to a nerve centre and then outward to an effector (as a muscle or gland) without reaching the level of consciousness (REFLEX)

Question 18

Reflexes vs voluntary movements

Answer 18

once reflexes they are released, they can’t be stopped vice versa for voluntary

Question 19

What is the Jendarssik manouvre?

Answer 19

clenching the teeth, making a fist, or pulling against locked fingers when having patellar tendon tapped > reflex becomes larger

Question 20

What control dominates on stretch reflex?

Answer 20

inhibitory

Question 21

What process reveals the excitatory control from supraspinal areas?

Answer 21

decerebration (the elimination of cerebral brain function by removing the cerebrum)

Question 22

What can result from brain damage giving over active or tonic stretch reflex?

Answer 22

rigidity

spasticity

Question 23

What is hyperreflexia?

Answer 23

overactive reflexes, loss of descending inhibition

Question 24

Is hyperreflexia associated with upper or lower motor neuron lesions?

Answer 24

upper motor neurons

Question 25

What is clonus?

Answer 25

Involuntary and rhythmic muscle contractions, loss of descending inhibition

Question 26

Is clonus associated with upper or lower motor neuron lesion?

Answer 26

upper motor neurons lesions

Question 27

What is the Babinski sign? Include +ve and -ve results.

Answer 27

sole stimulated with blunt instrument > -ve results big toe curls downward, +ve result big toe curls upward (abnormal in adults)

Question 28

What is hyporeflexia?

Answer 28

below normal or absent reflexes

Question 29

Hyporeflexia is associated with upper or lower motor neuron lesions?

Answer 29

lower motor neuron lesion